(138d) Pressure Induced Non-Linear Oscillations in Two-Phase LNG Pipe Flow

Two-phase fluid flows are often subject to pressure induced oscillations. Due to its compressibility the vapor bubbles act as a spring with an asymmetric non-linear characteristic. Compressing pressure fluctuations cause less displacement of the liquid mass than expanding pressure fluctuations.

The volume of the vapor bubbles increases or decreases differently if the pressure fluctuations are compressing or expanding. Consequently compressing pressure fluctuations in a two-phase pipe flow cause less displacement in the direction of the pipe flow than expanding pressure fluctuations.

The displacement depends on the ratio of LNG liquid to vapor, the ratio of pressure fluctuations over average pressure and on the exciting frequency of the pressure fluctuations.

The paper describes the governing non-linear equation for two-phase fluid oscillations and presents steady state solutions for free and for pressure induced oscillations. Resonance criteria and effects of LNG two-phase flows on plant safety and operation are discussed.